Theatergoers racing through Shubert Alley to make curtain time, beware! If you’re not careful, you might trip over all those wires piping lines to actors with memory lapses.

As I reported last week, Al Pacino, star of David Mamet’s “Moose Murders” — I mean “China Doll”— is being fed dialogue through his Bluetooth earpiece, with cables running to the seven — yes, seven! — teleprompters on the set.

Less forgivable is Bruce Willis, who sports an earpiece the size of a cellphone circa 1984 in “Misery.” He’s only 60, a spring chicken in Broadway years. Spies who’ve seen it say it feels like a play by Harold Pinter. The excellent Laurie Metcalf says a line and then there … is … a … pause before Willis responds.

“The script is changing and he’s nervous,” a source says. “But he’s working very hard.”

Metcalf is being extremely patient with her co-star. But she’s the one with the sledgehammer, so it might be wise for Willis to get off the f–king book!

Nobody will openly discuss the increasing prevalence of earpieces on Broadway. As one press agent says, “Theater is an illusion. And it’s all part of the magic that actors now look like they know their lines.” And yes, he snickered after he said that.

But everyone agrees: The technology is getting so good that at some point actors will be spared the drudgery of having to memorize the script.

We’ve come a long way from Mary Martin struggling through “Legends!” in 1986. Wearing a primitive earpiece during a Washington, DC, performance, she heard taxi dispatches instead of cues: “Take me to 1600 Pennsylvania Avenue, please!”

Marian Seldes had a small speaker installed in her bleacher chair on the set of “Deuce” in 2007. At an early preview there was an awkward pause. Marian turned to her chair and shouted, “What?”

Angela Lansbury, who’s open about using the devices, covered them up with Princess Leia-like hair muffins in 2009’s “Blithe Spirit.” She was brilliant, and the audience was none the wiser. But one night there was a glitch and Lansbury rode over co-star Jayne Atkinson’s laugh line. The next night, standing in the wings with Christine Ebersole, Atkinson said, “I wonder if Angie will step on my laugh line again tonight.” Ebersole replied: “We’d better check with Houston.”

Tyson is a master with the earpiece. She wore one in “A Trip to Bountiful,” and was fed not only lines but blocking. Did it matter? Not a bit. She won the Tony that year. One night, however, she paused and asked, “Wadie, Wadie — where are you?” “Wadie,” it turned out, was Wade, her feeder, whose voice in her ear had momentarily cut out.

If actors of a certain age need the devices to extend their glorious stage careers, fine. But they can too easily become crutches for Hollywood stars, who have to learn only a few pages of dialogue at a time for a film. But if they’re going to be even halfway decent on stage, they have to sustain a character over 100 pages — and that means learning the lines.

As for “China Doll,” I hear Mamet, who disappeared after the first preview, has returned to the Schoenfeld. But given the number of teleprompters on the set, maybe Pacino would be better served by a cable repairman than a playwright.

Lupita Nyong’o (left) stars in “Eclipsed” at the Public Theater. Joan Marcus

The Daily Mail of London raked Lupita Nyong’o over the coals this week, claiming she’s an “ice cold diva” who won’t have lunch with her fellow cast members in “Eclipsed,” now at the Public Theater, and refuses to speak to them when she’s not in character.

I nosed around and was told that Nyong’o is “shy” and “intense” but gets along quite well with her co-stars.

Producer Stephen Byrd, who’s moving “Eclipse” to Broadway in February, tells me, “The Daily Mail story is baseless and offensive — although, when I think of all the remarkable artists who had to endure misogynistic slurs, Lupita is in fine company. She is an inspiration onstage and off.”